1994 рік

The possibility of utilizing alkaline hydrolysis for studying changes in the properties of thermotropic liquid crystalline copolyester fibres is evaluated. The copolyester fibre manufactured from 4-hydroxybenzoic acid (HBA) and 2-hydroxy 6-naphthoic acid (HNA) in a molar ratio of 73/27 HBA/HNA was hydrolysed at 21°C with 2.5 M NaOH, 0.1% cetyltrimethylammonium bromide solution. After hydrolysis the shape of the HBA/HNA fibre cross-section changed from round to polygonal, unlike the cross-section of poly(ethylene terephthalate) fibre which does not change in shape after a similar treatment. Although heat treatment markedly increased the tenacity of HBA/HNA fibre, the tenacity fell steadily with increasing weight loss by hydrolysis. In contrast, the tenacity of the non-heat-treated fibre remained constant up to a weight loss of 58%, indicating that hydrolysis was occurring at the fibre periphery and leaving its core unaffected. For both the heat-treated and non-heat-treated products the initial modulus of the fibres fell progressively with increasing weight loss. Significant change in brittleness did not appear to occur when either form of HBA/HNA fibre was hydrolysed to a weight loss of 38%.

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In order to characterize the interface in polymer blends, a new method is suggested, in which the interface is exposed by selectively dissolving in solvent. By means of X-ray photoelectron spectrometry, we studied the molecular state in the interfacial area of graft copolymers of polyolefin and polar polymer. When the graft copolymers were used as compatibilizers, the backbone polymer and branch polymer diffused into the corresponding miscible polymer bulks. The specific interactions between some macromolecules were very strong; the small solvent molecule could not separate these macromolecules.

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Poly(vinyl alcohol) (PVA) Sloviol R was modified to different degrees by acetalization reactions with aldehyde (formaldehyde, acetaldehyde, propionaldehyde and n-butyraldehyde) for 6 h at 60°C in the presence of HCl as catalyst. Samples of the modified PVA were tested as dispersants in vinyl chloride suspension polymerization. The grains of poly(vinyl chloride) (PVC) powder produced are more compact, not very porous, have a higher bulk density and lower plasticizer absorption. By increasing the degree of acetalization, the bulk density of the PVC produced decreases. Using a mixture of commercial PVA Alcotex 72.5 (which produces porous PVC with a low bulk density) and acetalized PVA, PVC with a grain morphology can be obtained.

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A new method for studying molecular mobility in glassy polymers--the method of conformationally inhomogeneous probes--is described. A small quantity of a low-molecular-weight compound (probe) having unidentical conformations with different vibrational spectra is introduced into a polymer. The thermodynamic and activation parameters responsible for the concentrations of the conformers and the rates of conformational transitions are connected with both the intramolecular interactions and the properties of the medium (e.g. polymer). Information about the kinetics and equilibria of the conformers could be obtained by investigating the vibrational spectra. This information may be the key to understanding the molecular mobility and free-volume distribution in polymers. The following compounds were used as probes: 1,2-bromofluoroethane, methyl dichlorophosphate and trans-l,2-dichlorocyclohexane. The polymers polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(vinyl acetate), poly(vinylbutyral), polypropylene and polybutadiene were investigated. The temperature dependences of the absorption-band intensities of the probes were studied. Freezing of the conformational transitions in the probe molecules was found at temperatures Tf characterizing specific polymer-probe systems. The Tf are close to the temperatures of the relaxation transitions in the pure polymers. The possibilities of the method are discussed.

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We consider the four criteria recently proposed by one of us (JMG) for defining a thermoreversible gel and use them with syndiotactic polystyrene/solvent systems. We show that some of these systems, considered to be gels, do not obey these criteria. In addition, a simple mechanical test is presented which allows a thermoreversible gel to be recognized

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We report the elucidation of the surface morphology of a number of ABA triblock copolymers by atomic force microscopy (AFM). The chemical nature of the different phases observed in the image and the size of the respective domains was determined by image analysis. In this way the various features of the domain structure could be quantitatively determined and related to theory.

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The program AMBER 3.0 Rev.A has been used in a molecular mechanical study of two conformational models for the title compound on a simplified solid-state model with hexagonal coordination. Results show that the right-handed model is the minimum energy structure with a relative stability of 20 kcal mol-1 residue. Molecular dynamics trajectories show less torsion angle variability in the backbone than in the side chain, according to the packing environment of each residue

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This work deals with the bioactive agent release from dextran-~t-naphthylacetic and dextran-naproxen adducts, in which the bioactive agent is linked to the dextran carrier through a spacer. Water absorption characteristics of these adducts have been studied. The hydrolysis in the heterogeneous phase showed autocatalytic effects and the release of the active compound is dependent upon the hydrophilic character of the adduct as well as the pH value of the medium.

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Dynamic mechanical thermal analysis of some well defined poly(e.-caprolactone)-g-poly(methyl methacrylate)- co-polyurethane samples has been performed. The results show that the hard segment/soft segment phase separation of the polyurethane backbone is decreased with soft segment grafting and that all of the poly(methyl methacrylate) is mixed in with the poly(e.-caprolactone). These results confirm previous differential scanning calorimetry studies

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The crystallization of poly(ethylene terephthalate) has been followed in real time by measuring the dielectric complex permittivity. The measurements have been discussed by assuming the contribution to the dielectric losses of two types of amorphous phases: amorphous regions filling the interspherulitic space and amorphous regions located between crystalline lamellae within the spherulites. The deviation of the measurements from the calculated values assuming a simple two-phase model has been interpreted as being due to changes in the nature of the amorphous regions as crystallization proceeds. A phenomenological description of the experiments in terms of the Havriliak-Negami description permits the changes of the relaxation time distribution functions upon crystallization to be followed. The evolution with crystallization time of the derived dipole moment time correlation functions are discussed in the light of different models.

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